Transposing involves the shifting of music from one musical key signature to another. Thus music written in one key can be transposed up or down any selected number of half tones to sound in another key. Automatic transposition systems for keyboard musical instruments are well known. This has been done, for example, by mechanically shifting the keyboard relative to the mechanism that initiates a tone so that each key is set to produce a note of the transposed musical scale. In U.S. Pat. No. 3,610,800, for example, there is described a keyboard instrument in which key-operated switches are detected by using conventional time division multiplexing. By assigning each key-operated switch to a unique time slot in each repetitive scanning cycle, an actuated switch causes a pulse to appear in a predetermined time slot. Transposition is obtained by in effect shifting the pulses to other time slots by delaying or advancing the pulses with respect to the start of a multiplexing cycle.
Closely related to the concept of transposing is that of intramanual coupling in which the playing of one note on the keyboard generates, in addition to the normal tone, one or more additional tones at preselected scale intervals, such as an octave higher or lower. U.S. Pat. No. 3,697,661, for example, describes an intramanual coupler in which the keys are time-division multiplexed in conventional manner, coupling being obtained by delaying the keyed pulses and adding the delayed pulses to the input time-division multiplexed key pulses. The added pulses are delayed to other time slots, generating tones at preselected coupler intervals.